1. Field of the Invention
The present invention relates to a pivot assembly (hereinafter referred to as ass""y) bearing in which a fluorine-based oil composition is sealed up. More particularly, the present invention pertains to a pivot ass""y bearing in which a fluorine-based oil composition is sealed up, and which has low torque, low outgas, a long service life and excellent hysteresis characteristics.
2. Description of the Prior Art
In bearings for pivot ass""y, many studies have been recently made in order to develop bearings providing low torque, low outgas, a long service life and excellent hysteresis characteristics. The ability of recent computers has been improved because a variety of proposals have been made for high densification and high-speed performance to cope with a drastic increase in memory capacity and read velocity. At present, however, still much possibility for improvement remains.
It is an objective of the present invention to develop a pivot ass""y bearing for an apparatus which writes and reads out information in an information apparatus such as HDD (hard disc drive), FDD (floppy disc drive) memories, CDD (compact disc drive), MOD (magneto-optical disc drive) and the like of computer systems, said pivot ass""y bearing meeting requirements such as low torque, low outgas, a long service life and excellent hysteresis characteristics.
By the term xe2x80x9ca pivot ass""y bearingxe2x80x9d as used in the present invention is meant a bearing which is used to drive an actuator for writing and reading out information used in a peripheral information apparatus such as HDD (hard disc drive), FDD (floppy disc drive) memories, CDD (compact disc drive), MOD (magneto-optical disc drive) and the like of computer systems. The present invention has been contrived in order to provide a pivot ass""y bearing which is surpassingly excellent in low torque, low outgas, a long service life and excellent hysteresis characteristics compared to conventional pivot ass""y bearings.
Extensive studies have been made by the inventors on the development of bearings having such favorable characteristics as mentioned above, and as a result, found that good results are obtained when a fluorine-based oil composition which is characterized by comprising an additive of a specific chemical structure and a fluorine-based oil is sealed in a pivot ass""y bearing. The invention is accomplished based on the above finding.
A typical pivot ass""y bearing according to the present invention is illustrated in FIG. 1, wherein the symbols stand as described in the following:
1; outer race, 2; ball, 3; inner race 4; chamfered face of inner race, 5; retainer, 6; chamfered face of outer race, 7; shield, 8; snap ring, d; inside diameter of bearing, Li; diameter of inner race shoulder, Lo; diameter of outer race shoulder, D; outside diameter of bearing. Bearing space volume means the residual space volume obtained by subtracting the solid volumes of the balls and retainers from the space volume encompassed by the inner race, outer race and shield.
In addition, a magnetic disc apparatus which incorporates the pivot ass""y bearing according to the present invention is illustrated in FIG. 2, wherein the symbols stand as described in the following: 10; pivot shaft, 20; swing arm 30; magnetic head, 40; drive unit, 50; magnetic disc, 60; clamp, 70; rotational shaft of spindle motor, 80; housing.
When a drive pulse is entered into the magnetic disc apparatus, the drive unit 40 causes the swing arm 20 supported by the pivot shaft 10 to swing, and the magnetic head 30 radially traverses from the inner circumference to the outer circumference or vice versa so as to carry out reading or writing of information.
The swing angle of the swing arm 20 at the time of swinging is in the range of 20 to 30 degrees.
The hysteresis characteristics as mentioned in the present invention is the characteristic when the magnetic head 30 moves back and forth one time through the same route.